This invention addresses service disruptions in a telecommunications switch when subscriber lines are transferred (cutover) from existing line support equipment to different line support equipment. More specifically, the invention minimizes the disruption of subscriber selectable features during the transfer of line support equipment.
The transfer of equipment providing service to subscriber lines typically occurs in two ways: a set of subscriber lines being served by an existing switch may be desired to be transferred to a new switch; or a set of subscriber lines which is served by a switch with existing line unit equipment is desired to be transferred so that the same set of subscriber lines will be served by different line support equipment associated with the same switch. Where a new switch is to replace an existing switch, conventional analog subscriber lines are temporarily connected in parallel to both switches. The connections between the subscriber lines and the two switches are normally verified line by line to minimize the possibility of service interruptions when the service transition is made from the old switch to the new switch. The line by line verification is utilized to confirm that the same telephone number in both the old and new switch accesses the same subscriber line.
Such known test methods involving parallel connections to a subscriber line are not suitable for testing subscriber lines served by digital subscriber loop carrier facilities, such as the AT&T SLC.RTM. systems. A method for the pre-cutover verification of subscriber lines served by digital carder facilities involving a transition from an existing switch to a new switch is discussed in U.S. Pat. No. 4,653,043. When a transition of service for a set of subscriber lines from an existing switch to a new switch is required, the availability of two independently controllable switches provides flexibility with regard to implementing the transition.
Digital switches, such as the AT&T 5ESS.RTM. switch, are capable of supporting conventional analog subscriber lines through analog line unit equipment and are also capable of supporting subscriber lines via a multiplexed digital carrier line unit wherein communications with subscriber lines are provided by digital signaling within multiplexed time slots. A remote terminal, which includes multiplexing, A/D, and D/A functions, is used as an interface between the digital signaling carried by a multiplexed communications line and analog subscriber lines. Transition difficulties exist when subscriber lines are transferred from analog line units associated with the digital switch to digital carder line units associated with the same digital switch. One approach utilized for such a transition is to permit telephone numbers to remain associated with the subscriber lines coupled to the switch through existing analog line unit equipment and assign new telephone numbers for the same subscriber lines when service is transferred to the digital carrier line units. However, the assignment of new telephone numbers for subscribers is undesirable from a telephone customer perspective.
An alternative transition on the same digital switch from line unit equipment to digital carrier line unit equipment is to make a flash cut, i.e., simultaneous physical disconnection, of the line unit supported lines. A multiplexed T1 line is connected as quickly as possible between the digital carrier line unit equipment and a remote terminal which services the subscribers. This technique results in the subscribers losing the ability to use previously programmed customer selectable features until a substantial time period following the restoration of service. The data table which stored the selectable features must be updated following the cutover.
Thus, there exists a need for an improved method for making a service transition of existing subscriber lines from one type of line support equipment to a different type of line support equipment associated with the same telecommunication switch, such as from analog line unit equipment to digital carder line unit equipment.